1. Field of the Invention
The present invention relates to apparatus for determining the speed of an endless torque-transmitting member of a continuously variable transmission.
2. Description of the Related Art
Conical pulley transmissions having an endless torque-transmitting means and for providing a continuous change of the transmission ratio are increasingly utilized as automatic transmissions in motor vehicles. FIG. 1 of the drawings is a schematic representation showing the basic structure of such a transmission.
A continuously variable transmission of the type shown in FIG. 1 includes two conical pulley pairs 4 and 6. One conical pulley disc 41 of conical pulley pair 4 is rigidly connected with a drive shaft 8 that is driven by, for example, an internal combustion engine. The other conical pulley disc 42 of conical pulley pair 4 is non-rotatably connected with but is axially moveable relative to drive shaft 8. One conical pulley disc 61 of conical pulley pair 6 is rigidly connected with an output shaft 10 that drives the vehicle. The other conical pulley disc 62 of conical pulley pair 6 is non-rotatably connected with but is axially moveable relative to output shaft 10. An endless torque-transmitting means 12 passes around the two conical pulley pairs 4 and 6 and is in frictional engagement with the opposed two conical surfaces of the respective conical pulley pairs. By means of opposite adjustment of the axial spacing between the two conical pulleys of each conical pulley pair, the rotational speed relationship between the two conical pulley pairs, and therefore the transmission ratio of the transmission, can be changed.
Pressure chambers 14 and 16 that are connected by way of hydraulic conduits 18 and 20 with a control valve 22 serve, for example, for the adjustment of the transmission ratio by the application to pressure chambers 14 and 16 of pressurized hydraulic fluid pressure, by which the transmission ratio can be controlled. A control unit 23 serves for the actuation of the control valve 22 and includes a microprocessor with associated storage means. Inputs for the control unit are connected, for example, with a selection lever unit that serves for operating the transmission, an accelerator pedal, rotational speed sensors, and the like. The outputs of the control unit are connected, for example, with a clutch, a power output stage of the engine (not shown) and control valve 22. The construction and function of a continuously variable transmission are known and are therefore not further explained.
For many applications it is advantageous to know the speed of endless torque-transmitting means 12, for example in order to precisely establish the contact pressure applied by the conical surfaces of the conical pulleys with which the endless torque-transmitting means is in contact, and which is controllable by the pressure in pressure chambers 14 and 16. That contact pressure should only be as large as necessary for acceptable frictional engagement or power flow between the endless torque-transmitting means and the conical pulleys, so that the transmission is not unnecessarily stressed and so that no unnecessary hydraulic pumping capacity is utilized.